Performance of Vibration Power Generators Using Single Crystal and Polycrystal Magnetic Cores of Fe–Ga Alloys

The performance of a vibration power generator using a single crystal core of Fe–Ga alloy was compared with that of a generator using a Fe–Ga alloy polycrystal core with a similar Ga concentration. When the generator using the polycrystal core was forcibly vibrated by 1-G acceleration, the vibration frequency dependence of the open-circuit voltage showed a peak with a maximum value of about 0.14 V at the first resonance frequency due to the inverse magnetostrictive effect. On the other hand, the generator using a single crystal core with a <100> direction parallel to the external stress direction exhibited a maximum value of about 0.26 V, about two-times larger than that of the device using the polycrystal core. Consequently, a vibration energy generator using a single crystal core of Fe–Ga alloy has advantages in performance over a generator using a polycrystal core.

Morphology and Genesis of Ballas and Ballas-Like Diamonds

Ballas diamond is a rare form of the polycrystalline radial aggregate of diamonds with diverse internal structures. The morphological features of ballas diamonds have experienced repeated revision. The need that this paper presents for development of a crystal-genetic classification was determined by a rich variety of combined and transitional forms of ballas-like diamonds, which include aggregates, crystals, and intergrowths. The new crystal-genetic classification combines already-known and new morphological types of ballas as well as ballas-like diamonds discovered in the placers of Yakutia, the Urals, and Brazil. The ballas-like diamond forms include spherocrystals, aggregates with a single crystal core, split crystals, radial multiple twin intergrowths, and globular crystals. The crystal genetic scheme of the evolution of ballas and ballas-like diamonds is a sequence of the morphological types arranged in accordance with the conventional model of the dependence of the mechanism and diamond growth from carbon supersaturation developed by I. Sunagawa. The evolution of the growth forms of ballas and ballas-like diamonds was tracked based on the macrozonal structure of diamonds varying from a flat-faced octahedron to a fibrous cuboid with its transition forms to the radiating crystal aggregates. The morphological diversity of the ballas-like diamonds depends on the level of supersaturation, and abrupt changes of the level of supersaturation engender abrupt changes in a mechanism of crystal growth. The change in the rate of growth under the influence of adsorption and absorption of the mechanic impurities accompanied the sudden appearance of the autodeformation defects in the form of splitting and multiple radial twinning of crystals. The spherical shape of Yakutia ballas-like diamonds is due to the volumetric dissolution that results in the curved-face crystals of the “Urals” or “Brazilian” type associated with ballas diamonds in placers.

Surface-Only Spectroscopy for Diffusion-Limited Systems Using Ultra-Low Temperature DNP MAS NMR at 16.4 T

Conventional dynamic-nuclear-polarization (DNP) technique at T ~100 K can enhance sensitivity of magic-angle spinning (MAS) NMR over 100-fold for standard samples containing urea/proline at high-field conditions, B0= 9.4–16.4 T. In the scene of real applications, however, the achievable enhancement is often much lower than for urea/proline due to faster 1H relaxation (T1H) promoted by molecular-segmental fluctuations and methyl-group rotations active even at low temperatures, hindering an efficient polarization diffusion within the system. Here, we show at 16.4 T that ultra-low temperature (T≪100 K) provides a general way to improve the DNP efficiency for such diffusion-limited systems as we demonstrate on microcrystalline sample of a tripeptide N-f-MLF-OH. In a further step, the hyperpolarization localized at the crystal surface enabled “surface-only” spectroscopy eliminating background signals from the crystal core. The surface-only data, rather than the currently popular surface-enhanced data, should prove to be useful in many applications in biological and material sciences.

Surface-Only Spectroscopy for Diffusion-Limited Systems Using Ultra-Low Temperature DNP MAS NMR at 16.4 T

Conventional dynamic-nuclear-polarization (DNP) technique at T ~100 K can enhance sensitivity of magic-angle spinning (MAS) NMR over 100-fold for standard samples containing urea/proline at high-field conditions, B0= 9.4–16.4 T. In the scene of real applications, however, the achievable enhancement is often much lower than for urea/proline due to faster 1H relaxation (T1H) promoted by molecular-segmental fluctuations and methyl-group rotations active even at low temperatures, hindering an efficient polarization diffusion within the system. Here, we show at 16.4 T that ultra-low temperature (T≪100 K) provides a general way to improve the DNP efficiency for such diffusion-limited systems as we demonstrate on microcrystalline sample of a tripeptide N-f-MLF-OH. In a further step, the hyperpolarization localized at the crystal surface enabled “surface-only” spectroscopy eliminating background signals from the crystal core. The surface-only data, rather than the currently popular surface-enhanced data, should prove to be useful in many applications in biological and material sciences.

Polyol-Made Luminescent and Superparamagnetic β-NaY0.8Eu0.2F4@γ-Fe2O3 Core-Satellites Nanoparticles for Dual Magnetic Resonance and Optical Imaging

Red luminescent and superparamagnetic β-NaY0.8Eu0.2F4@γ-Fe2O3 nanoparticles, made of a 70 nm-sized β-NaY0.8Eu0.2F4 single crystal core decorated by a 10 nm-thick polycrystalline and discontinuous γ-Fe2O3 shell, have been synthesized by the polyol process. Functionalized with citrate ligands they show a good colloidal stability in water making them valuable for dual magnetic resonance and optical imaging or image-guided therapy. They exhibit a relatively high transverse relaxivity r2 = 42.3 mM−1·s−1 in water at 37 °C, for an applied static magnetic field of 1.41 T, close to the field of 1.5 T applied in clinics, as they exhibit a red emission by two-photon excited fluorescence microscopy. Finally, when brought into contact with healthy human foreskin fibroblast cells (BJH), for doses as high as 50 µg·mL−1 and incubation time as long as 72 h, they do not show evidence of any accurate cytotoxicity, highlighting their biomedical applicative potential.